I was reading a health column in the Seattle Times about a man who used cornmeal to help his toenail fungus and the doctor replied that he had heard from gardeners who used cornmeal on their roses to control black spot and powdery mildew because apparently cornmeal has some fungicidal properties.
Has anyone heard of this or tried it? On their roses, I mean.
I've heard of people using baking soda to control black spot, etc, and I've heard of corn gluten (not the same thing as cornmeal) as a preemergent herbicide, but never heard of cornmeal as an anitfungal.
I've used it, and it seems to work, though not all the times. I rotate through a number of organic control methods, and sometimes there is no rhyme or reason why one works one season, but not the next. Check out the website (I hope I remembered it correctly...) http://www.dirtdoctor.com
I sprinkle cornmeal on the ground under my rose and crepe myrtle to help with powdery mildew. I also steep about 1 cup of cornmeal in a gal. of water, then use the "cornmeal tea" to spray on my crepe myrtle to get rid of powdery mildew. Haven't tried it on my rose bush, tho.
The cornmeal works on the toe fungus, but it's a slow acting cure.